The On-Line Encyclopedia of Integer Sequences (OEIS)

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A061309

a(n) is the smallest number required to make the concatenation of a(n) and 2n+1 a prime, or -1 if no such number exists.
(history; published version)

#4 by N. J. A. Sloane at Thu Dec 05 19:54:50 EST 2013

AUTHOR

_Amarnath Murthy (amarnath_murthy(AT)yahoo.com), _, Apr 26 2001

Discussion

Thu Dec 05

19:54

OEIS Server: https://oeis.org/edit/global/2075

#3 by R. J. Mathar at Tue May 07 09:55:24 EDT 2013

STATUS

editing

approved

#2 by R. J. Mathar at Tue May 07 09:55:20 EDT 2013

EXTENSIONS

More terms from _Frank. Ellermann(AT)t-online.de, _, Jun 15 2001

STATUS

approved

editing

#1 by N. J. A. Sloane at Fri May 16 03:00:00 EDT 2003

NAME

a(n) is the smallest number required to make the concatenation of a(n) and 2n+1 a prime, or -1 if no such number exists.

DATA

1, 0, 0, 0, 1, 0, 0, -1, 0, 0, 4, 0, -1, 1, 0, 0, 2, -1, 0, 1, 0, 0, -1, 0, 1, 1, 0, -1, 1, 0, 0, 1, -1, 0, 2, 0, 0, -1, 2, 0, 1, 0, -1, 4, 0, 1, 1, -1, 0, 1, 0, 0, -1, 0, 0, 2, 0, -1, 1, 3, 3, 1, -1, 0, 1, 0, 4, -1, 0, 0, 2, 2, -1, 5, 0, 0, 1, -1, 0, 4, 2, 0, -1, 0, 3, 1, 0, -1, 4, 0, 0, 13

OFFSET

0,11

COMMENTS

a(0) = 0 for a prime.

EXAMPLE

a(9) = 0 as 19 itself is a prime; a(10) = 4 as 421 is a prime but 121, 221, 321 are not.

KEYWORD

sign,base

AUTHOR

Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 26 2001

EXTENSIONS

More terms from Frank.Ellermann(AT)t-online.de, Jun 15 2001

STATUS

approved